1. Field of the Invention
This invention relates to processes for increasing the relative viscosity (RV) of a reactant polyamide through the use of chain extender compounds and to polyamide products incorporating chain extender moieties in their polyamide chains.
2. Description of Related Art
Various methods have been proposed to impart high viscosity to polyamides.
Catalysts are employed to speed up the reaction. For example, polyamide 6,6 synthesis involves the reaction of a diamine (hexamethylene diamine) and a diacid (adipic acid) to produce the polyamide 6,6 and water. The rate of formation of the polyamide depends greatly on the removal of water from the reaction system. Catalysts do speed up the reaction but water removal remains the rate determining factor.
Another method to impart a high viscosity to polyamides is referred to as chain extension. Chain extension is based on a reaction between a polyamide chain end group (an acid end group or an amine end group) and a chain extender molecule with two reactive end groups that react with either the amine end group or the acid end group of the polyamide to connect two polyamide chains. Prior use of chain extenders with polyamides did not increase RV enough to adopt the technology. The use of bis-lactams for polyamidation acceleration was disclosed by Flory in U.S. Pat. No. 2,682,526.
There is a need to take low RV polyamide and rapidly increase its RV to a predictable final product with a higher RV.
These and other objects of the invention will be clear from the following description.